In Situ Measurement of the γ/γ′ Lattice Mismatch Evolution of a Nickel-Based Single-Crystal Superalloy During Non-isothermal Very High-Temperature Creep Experiments

Creep of a nickel-based single-crystal superalloy during very high-temperature jumps followed by synchrotron X-ray diffraction

“…The final level of d ? may then be lower, the same or higher than the initial one [49]. Small temperature excursions generally result in a decrease of d ?…”

“…the c/c 0 interface dislocation network stability, the dislocation density in the c and c 0 phases and the volume fraction of the strengthening c 0 phase, in order to explain the subsequent macroscopic strain rate and amplitude. To do so, non-isothermal experimental conditions ("positive" and "negative" thermal cycling) leading to the entry of dislocations in the c 0 phase are especially performed and followed by in situ X-ray diffraction (XRD) under synchrotron radiation avoiding then any uncertainties in post mortem measurements due to unloading (stress relaxation) or cooling (changes in the volume fraction of both phases) processes [48,49]. This technique allows a better understanding of the physical mechanisms of plastic strain in superalloys and more specifically how each phase is deformed during non-isothermal creep loading by giving access to the internal stresses.…”

Development and use of a new burner rig facility to mimic service loading conditions of Ni-based single crystal superalloys

“…Nevertheless, this model with its additional internal variable is the only one able to capture complex microstructural phenomena such as dissolution/precipitation of strengthening particles, dislocation recovery processes and their impact of the mechanical behavior. Under very complex conditions such as the ones presented in this article, this model performs better than any other model where the temperature dependence is only taken into account through the temperature dependence of the material's coefficients [7,8].…”

“…Polystar was particularly developed for complex non-isothermal loadings. This model takes into account microstructural changes which can occur in the material such as γ precipitation/dissolution and dislocation recovery processes induced by the temperature history seen by the material, especially close to the γ solvus temperature [7]. The model was calibrated using isothermal and nonisothermal creep tests performed on MC2 samples having a stress axis close to the [001] crystallographic direction (deviation less than 8 degrees).…”

Measurement of the effective γ/γ′ lattice mismatch during high temperature creep of Ni-based single crystal superalloy

“…This is however the main strength of in-situ TCD measurement during creep experiments. It allows a measurement of δ ⊥ during transient phenomena upon thermal or mechanical loading [29,30,32,48,53], in addition to a very good precision and the quite large analyzed volume (0.1x0.5x 3.4 mm 3 ). The two main difficulties of this technique are the synchrotron source access and the necessity of a very specific creep testing machine [37].…”